Deflection transducer for measuring vehicle loads and a system for mounting same

ABSTRACT

A transducer which includes a central portion (12) having two longitudinally extending parallel rigid beam members (14,16) and two transverse parallel flexure members (30,32) which extend between the two rigid beam members (14,16) at right angles thereto. The rigid beam members (14,16) include end element portions (18,20). Flexure joints (58,60) and mounting portions (62,64) are located longitudinally outboard of the flexure joints (58,60). The flexure members (30,32) each include two cutout portions (34,36,40,42) defining flexure points. Strain gauges (46,48,50,52) are placed in the vicinity of the cutout portions (34,36,40,42) and are electrically connected into a bridge to produce an electrical signal output indicative of the load on the vehicle. The transducer is mounted by means of a mounting element (79) which includes two opposing mounting pad portions (82,84) and an intermedicate center portion (86). The mounting pad portions (82,84) are secured to a base member (87) on the vehicle, and then the center section (86) is removed, with the transducer then being securely and precisely connected between the two remaining mounting pad portions (82,84).

This is a divisional of application Ser. No. 479,842, filed on Feb. 13,1990 now abandoned.

TECHNICAL FIELD

This invention relates generally to the load measuring transducer art,and more specifically concerns deflection transducers for measuringvehicle loads and mounting means therefor.

BACKGROUND ART

Deflection transducers, such as that shown and described in U.S. Pat.No. 4,042,049 to Reichow, et al., have in the past been used to measurevehicle loads. Such transducers have been manufactured in various formsand configurations, and, in use, are typically positioned on astructural member of the vehicle such as an axle or a structural part ofthe suspension system. The purpose of using a deflection transducer insuch a manner is to obtain a fast and accurate "on-board" indication ofvehicle load weight. An onboard weighing system permits convenientmeasurement of loads at any time, without the necessity of using aconventional scale, at the time of initial loading, or when part of theoriginal load is removed from the vehicle or when a partial new load isadded. An onboard system prevents accidental overloads and the possiblefines and other inconvenience associated therewith, while insuring thatthe vehicle is loaded substantially to its permitted capacity wheneverpossible.

However, conventional onboard weighing systems, including the systemshown in the '049 patent, are typically subject to inaccurate orfluctuating results, due to twisting and possibly other movements of thetransducer structure caused by normal movement of the vehicle. Suchmovements are not indicative of vehicle load, but do have an effect ontransducer output. Such transducers have also been found to be subjectto damage and breakage due to the typically harsh operating environmentsof such systems, such as, for instance, a logging truck.

Hence, there is a need for a rugged deflection transducer capable ofoperating in harsh on-board vehicle environments and designed so that itis not responsive to twisting movements, but substantially only totensile and compression deflection, which provides the desired accurateindication of vehicle load.

The mounting of such transducers is also an important factor relative tothe accuracy of the transducer results and its performance in general.Specialized devices are known, such as shown in U.S. Pat. No. 4,102,031to Reichow, et al., for insuring that the mounting elements for thetransducer are spaced apart a selected distance and have a particularconfiguration in order to properly receive the transducer. However,present devices, including the one shown in the '031 patent, and thedescribed methods for their use, have not provided completelysatisfactory results, as imprecise positioning of the mounting elementscan still occur, which in turn will result in poor performance of thetransducer when the transducer is connected to the mounting elements.

Hence, there is also a need for a transducer mounting structure whichwill insure precise positioning of the transducer structure.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention is a transducer for measuring vehicleloads, including two rigid, substantially parallel beam members, whichextend toward each other from opposing end element portions of thetransducer, and at least one flexure member which has flexure portionsand which extends between and is attached to said rigid members, whereinthe flexure members are sensitive to axial tension and compressionforces, but relatively insensitive to twisting forces. The transducerfurther includes strain sensing means secured to the flexure member inthe vicinity of the flexure portions thereof, providing an electricalsignal output corresponding to the axial deflection of the flexuremember and hence an indication of the load on the vehicle.

In another feature of the present invention, a mounting member for adeflection transducer is provided, wherein the transducer includesfastening means a predetermined distance apart. The mounting member is arigid, one-piece mounting element which includes mounting pad portionslocated at opposite ends of the mounting element and an intermediatecenter portion extending therebetween. The mounting pad portions includea lower surface which is adapted to be permanently secured to a basemember on a vehicle or the like, wherein the mounting pad portionsfurther include receiving means for the fastening means on thetransducer, to permit attachment of the transducer to the mountingmember and wherein the mounting member is adapted and configured so asto permit the convenient removal of a center portion thereof withoutchanging the distance or the alignment between the respective mountingpad portions prior to the attachment of the transducer to the mountingmember.

In yet another feature of the present invention, a method of mounting adeflection transducer on a structural base member such as a vehicle orthe like is provided, wherein the transducer includes first and secondspaced-apart fastening means. The method includes the initial step ofsecuring a one-piece mounting member to the base member, wherein themounting member includes mounting pad portions at opposite ends thereofand an intermediate center portion extending therebetween, the mountingpad portions including means for receiving, respectively, the first andsecond fastening means of the transducer. In the next step, the centerportion of the mounting member is removed, leaving the two mounting padportions secured to the base member, wherein the mounting pad portionsretain their initial exact orientation relative to each other followingthe removal of the center portion. The third step is securing thetransducer to the mounting pad portions by the fastening means on thetransducer and the receiving means on the mounting pad portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of the transducer of the present invention.

FIG. 2 is a side elevational view of the transducer of FIG. 1.

FIG. 3 is a schematic view showing the mounting element of the presentinvention secured to a structural member, as a result of the first stepin the process of mounting the transducer of FIG. 1.

FIG. 4 shows the result of the second step in the transducer mountingprocess of the present invention, using the mounting element of FIG. 3.

FIG. 5 shows the third step in the transducer mounting process of thepresent invention, in which the transducer of FIG. 1 is attached to theremaining mounting structure shown in FIG. 4.

FIG. 6 shows one mounting position for the transducer of the presentinvention on a vehicle.

FIG. 7 shows another mounting position for the transducer of the presentinvention on a vehicle.

FIG. 8 shows the use of the transducer of the present invention in afront end loader type of vehicle.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1 and 2 show the transducer 10 of the present invention. In use,the transducer 10 will typically be mounted on a structural portion ormember of a vehicle such as a tractor/trailer combination or a refusetruck, in order to measure the load thereon. Examples of particularlocations for mounting the transducer are shown in FIGS. 6, 7 and 8 andare explained in more detail in the following paragraphs. FIGS. 3-5 showa sequence of steps in the mounting of the transducer on the vehicle anda particular mounting element used therefor. These steps and themounting element are also explained in more detail in followingparagraphs.

Referring to FIG. 1, the transducer 10 includes a central body portion12. The body portion 12 in the embodiment shown includes two parallelrigid beam elements 14 and 16 which extend in the longitudinal directionof the transducer 10. The rigid beam elements 14,16 include end portions18 and 20 which define the opposing ends of central body portion 12, andwhich, in the embodiment shown, are circular in configuration,approximately 1" in diameter and are arranged at right angles to thebeam elements 14,16. The rigid beam elements 14,16 in the embodimentshown are each approximately 11/8 inches long by 1/2 inch wide andapproximately 1/8 inch thick. The outer surface of each beam element,i.e. surface 22 of beam 14, is curved to match the curved peripheraledge of its associated end portion. The beam elements 14 and 16 areseparated by approximately 1/2 inch, extending toward and overlappingeach other by approximately 5/8 inch. The configuration and the materialof the beam elements 14,16 are such that the beam elements aresubstantially rigid.

Connecting the two beam elements 14 and 16 in the embodiment shown aretwo parallel flexure elements 30 and 32. While the embodiment of FIGS. 1and 2 show two flexure elements, it should be understood that a greaternumber of flexure elements could be used. Also, in some applications, asingle flexure element could be used. The flexure elements 30 and 32extend, respectively, at right angles from the free ends of therespective beam elements 14 and 16 to the opposing beam element. Theflexure elements 30 and 32 are parallel to each other, are approximately1/2 inch apart and approximately 1/2 inch long. Flexure elements 30 and32 and outermost portions of beam elements 14 and 16 define anapproximately square central opening 37 in central body portion 12.

the surfaces of flexure elements 30 and 32 which face opening 37 arereferred to as interior surfaces. In interior surface 34 of flexureelement 30 are two cutout portions 36 and 38 in the form of semicirculargrooves which extend for the full width of flexure element 30. Similarcutout portions 40 and 42 are provided in the interior surface 43 offlexure element 32. Interior surfaces 34 and 43 face each other. Thethickness of the respective flexure elements 30 and 32 at the cutoutportions is approximately 1/32 inch. It is these relatively thinportions which provide the required flexing capability for flexureelements 30 and 32.

Mounted on the opposing exterior surface 44 relative to interior surface34 of flexure element 30 are two conventional strain gauge elements 46and 48. These are mounted at approximately the point where the flexureelement 30 is the thinnest, i.e. behind the cutout portions thereof. Ina similar fashion and position, strain gauges 50 and 52 are mounted onthe exterior surface 53 of flexure element 32. Strain gauges 46, 48, 50,and 52 are adapted to measure the axial tension and compression loads onthe flexure elements 30 and 32, due to the load on the vehicle. Theparticular transducer arrangement shown is resistant to twisting andbending loads, such that the movement of the flexure elements 30 and 32is due substantially only to axial tension and compression loads andthus is accurately reflective of the actual vehicle load.

In the embodiment shown, each of the strain gauges produces anelectrical output. The strain gauges are connected in the form of aconventional Wheatstone bridge with gauges 48 and 50 being in tension,while gauges 46 and 52 are in compression. The electrical output fromthe strain gauges is applied through leads (not shown) to the Wheatstonebridge arrangement (not shown) which is positioned in a cavity 57 in onemounting portion of the transducer. The bridge output signal is appliedto an external connector 56 at one end of the transducer. An electricalconnector line extends between the transducer, in particular theconnector 56 and a vehicle onboard computational electronics and displayelement (not shown) which will provide the actual indication of loadweight. The computational circuit and the display, typically located inthe vehicle cab, are conventional and therefore not discussed in detailherein.

Besides the central body portion 12, the transducer includes twotransducer flexure joints 58 and 60, which are located immediatelyoutboard from end portions 18 and 20 of central body portion 12. Theflexure joints 58 and 60 are defined by shallow lateral grooves in thebody of the transducer. The grooves are approximately 1/8 inch wide and1/32 inch - 1/16 inch deep, such that the diameter of the transducerbody at those points is approximately 7/8 inch. Immediately outboard offlexure joints 58 and 60 are transducer mounting portions 62 and 64,which are cylindrical in general configuration, extending in thelongitudinal direction of the transducer, with each mounting portionincluding two opposing flat sections through which lateral openings areprovided. Flat sections 69 and 71 are provided in mounting portion 62with opening 70 extending therethrough, as shown in FIGS. 1 and 2. Flatsections 69 and 71 extend for the full length of mounting portion 62,approximately 1 inch. Flat sections 75 and 77 in mounting section 64extend for approximately 3/4 inch from the inboard end thereof (adjacentflexure joint 60), with opening 72 extending therethrough. Mountingportion 64 extends for another 1 inch beyond the outboard end of theflat sections 75 and 77, accommodating the cavity 57 which houses theWheatstone bridge circuit.

In the embodiment shown, the entire transducer 10, including the centralbody portion, the flexure joints and the mounting portions comprises asingle piece of material, such as steel or aluminum, machined inaccordance with the above specifications. It should be understood,however, that the transducer may be constructed somewhat differentlywithin the spirit of the invention.

The transducer of the present invention further includes a system forsealing the central body portion against environmental hazards such asweather and the like. It includes a cylindrical tube element 80approximately 2.2 inches long, which is substantially the same length asthe combined length of the central body portion 12 and the two flexurejoints 58 and 60. The interior diameter of the tube 80 is slightlygreater than the exterior diameter of end portions 18 and 20. O-rings 81and 83 are positioned in the grooves comprising flexure joints 58 and 60and are slightly compressed when the tube 80 is fitted into place overthe body portion 12, thereby firmly holding the tube 80 in place. Theinterior space between the tube 80 and the body portion 12 of thetransducer is typically filled with gel material 85 in order to provideadditional environmental protection.

As indicated above, it is extremely important to the proper operation ofa transducer such as that described above, that it e mounted withprecision. In practice, precise mounting of such transducers has provento be difficult to achieve. FIGS. 3, 4, and 5 show a method and a deviceused to achieve a precise mounting of the transducer of FIGS. 1 and 2.FIG. 3 shows the mounting element 79 of the present invention. Mountingelement 79 includes in the embodiment shown two mounting pad portions 82and 84 at the opposing ends thereof, and a center portion 86 whichconnects the two mounting pad portions 82 and 84. The mounting element79 is elongated, approximately 4 inches long at its longest point,approximately 11/4 inches high at its highest point and approximately5/16 inches thick. Mounting element 79 is quite rigid and is made out ofsteel or similar material.

The center portion 86 is approximately 7/8 inch high, so that when themounting element 79 is in its upright position, as shown in FIG. 3,there is a small space between the center portion 86 and a base member87 on which the mounting element 79 rests. Each of the mounting padportions 82 and 84 have openings 88 and 90 therethrough, which canaccommodate a mounting bolt or the like. In the embodiment shown, theopenings 88,90 have a diameter of 5/16 inch. Also in the mountingelement 79 are a pair of cutout portions 92,94 at the extreme ends ofthe center portion 86, such that there remains only relatively thinsections of the center portion 86 at the top and bottom of cutoutportions 92 and 94.

In order to mount the transducer of FIGS. 1 and 2 on a base member suchas a vehicle using the mounting element 79, mounting element 79 is firstsecured to the base member 87 by welding the bottom edge of eachmounting pad portion 82 and 84 to the base member. This provides astrong, secure attachment of the mounting element to the base member.

Next, the center portion 86 of the mounting element is removed. Thecutout portions 92,94 are helpful since a substantial amount of materialwhich would otherwise have to be cut through is eliminated. After centerportion 86 is removed, only the two mounting pad portions 82 and 84remain, as shown in FIG. 4. However, mounting pad portions 82 and 84 doremain in the same precise relative position as when the mountingelement 79 as a whole was secured to the base member.

FIG. 5 shows the next and final step in the process for mounting thetransducer 10 to the mounting pad portions 82 and 84. The mounting isaccomplished by means of conventional bolts 96 and 98. The bolts extendthrough the openings 70 and 72 in the transducer and also through theopenings 88 and 90 in the mounting pad portions 82 and 84. The flatsections 69 and 75 abut the vertical surfaces 99,101 of the mounting padportions. A nut is attached to each of the threaded bolts and tightenedon the bolts so that the transducer 10 is securely attached to themounting pad portions. It should be understood, however, that otherfastening means besides bolts could be used to physically secure thetransducer 10 to the mounting pad portions.

The advantage of the mounting process shown in FIGS. 3 through 5 is thatthe mounting pad portions to which the transducer is attached maintain aprecise alignment during the securing of the mounting element as a wholeto the base member. The configuration of the mounting element and theprocess itself eliminates any necessity of having to align and realignthe two mounting pad portions during installation thereof.

At the conclusion of the process shown in FIGS. 3 through 5, thetransducer is mounted and ready for operation. A load on the vehiclewill cause the transducer to flex in both tension and compression,focused in the area where the strain gauges 46, 48, 50, and 52 aremounted on the flexure beam portions of the transducer. The bendingeffect on those flexure points will be due substantially entirely toaxial tension and compression, and not to bending and twisting moments.Hence, an accurate indication of the load is much more likely than withprevious systems which were subject to said twisting moments.

FIGS. 6, 7, and 8 show three possible locations for mounting thetransducer of the present invention on a vehicle. FIGS. 6 and 7 show theuse of the transducer in two different locations on a tractor/trailer.FIG. 6 shows the transducer 100 mounted directly on the upper surface102 of a front axle 104 of a truck. This arrangement will measure loadson the front axle. FIG. 7 shows a transducer 108 mounted on a portion ofthe suspension system of the trailer portion of the vehicle. FIG. 7shows simply an equalizer hanger element 110 and equalizer 112. In theembodiment of FIG. 7, the transducer 108 is mounted on the lower surfaceof the equalizer 112. The transducer arrangement shown in FIG. 7 willmeasure loads on the tandem axles to which the suspension system of FIG.7 is connected.

FIG. 8 shows the transducer of the present invention mounted on theforward lift arms 116 of a refuse truck 117. Such a vehicle will havelift arms on both sides of the cab 118 of the truck. Possible locationsfor the transducer are shown in FIG. 8. Two possible transducerlocations are shown. Transducer 120 is shown on the interior surface ofan intermediate section of the lift arm 116 while transducer 122 isshown on a forward section of the lift arm. One deflection transducerwill be mounted on each lift arm. The deflection of the arm 116 at aparticular point in the lift cycle is proportional to the weight of acontainer 164 being lifted (and dumped), and thus would be measured bythe transducer.

Other locations on various vehicles may certainly also be used for thetransducer of the present invention.

Although a preferred embodiment of the invention has been disclosedherein for illustration, it should be understood that various changes,modifications, and substitions may be incorporated in such embodimentwithout departing from the spirit of the invention as defined by theclaims which follow:

I claim:
 1. A transducer for measuring vehicle loads, comprising:tworigid, substantially parallel, spaced-apart beam members, extendingtoward and overlapping each other from opposing end element portionsthereof in a longitudinal direction of the transducer; at least twoflexure members, having flexure portions, said flexure members extendingbetween and attached to said rigid beam members, spaced apart in thelongitudinal direction of the transducer, said flexure members beingsensitive to axial tension and compression forces but relativelyinsensitive to twisting forces; and strain sensing means secured to saidflexure members in the vicinity of the flexure portions thereof,providing an electrical signal output corresponding to the axialdeflection of the flexure members and hence an indication of the load onthe vehicle.
 2. An apparatus of claim 1, wherein the at least twosubstantially parallel flexure members extend between said rigid beammembers at substantially right angles thereto, wherein the flexureportions in each flexure member include at least two cutout portionswhich extend across the width thereof, and wherein the strain sensingmeans are located in the vicinity of said flexure portions.
 3. Anapparatus of claim 2, wherein the transducer includes mounting portionswhich extend away from the end element portions of the rigid beammembers, and wherein the two mounting portions include openings thereinfor attachment of the transducer to a mounting member.
 4. An apparatusof claim 3, including a narrow flexure joint between the end elementportions of the rigid beam members and the mounting portions of thetransducer.
 5. An apparatus of claim 4, wherein the thickness of the endelement portions is approximately equal to the thickness of the flexurejoints.
 6. An apparatus of claim 2, wherein the two rigid members extendin the longitudinal direction of the transducer while the flexuremembers extend in the lateral direction thereof.
 7. An apparatus ofclaim 6, wherein one flexure member extends from an otherwise free endof one rigid beam member, while the other flexure member extends from anotherwise free end of the other rigid beam member.
 8. An apparatus ofclaim 2, wherein there is a substantial distance between the flexuremembers and end portions of the rigid beam members.
 9. An apparatus ofclaim 8, wherein the distance between the flexure members issubstantially equal to the distance between the flexure members and theend portions of the rigid beam members and to the distance between therigid beam members.
 10. An apparatus of claim 1, including means forsealing the rigid beam members and the flexure members against theenvironment.
 11. An apparatus of claim 10, wherein the sealing meanscomprises a pair of "O" rings positioned in the flexure joints and atube-like element which extends between the two "O" rings, the internaldiameter of the tube-like element being of such a size relative to thediameter of the "O" rings that the "O" rings are in compression when thetube element is in place.
 12. An apparatus of claim 11, wherein the areabetween the tube-like member and the transducer is filled with gel.